1. Field of the Invention
The present invention relates to a thick film forming process, specifically a thick film forming process which is effective in studying and developing circuits utilizing thick film patterns.
2. Related Background Art
The thick film forming process is classified largely into two types. One of them is screen printing, which is commonly used. The other is direct writing, which is suitable for small quantity production.
The first step in the screen printing is to design a circuit pattern and make a mask (screen) containing the open pattern based on the designed circuit pattern. Then, using the thus prepared masks, paste for a conductor, dielectric or resistor, etc. is printed on a substrate. It usually takes about one week to make the mask in the screen printing, and the screen printing is unsuitable for cases in which pattern changes are frequent.
On the other hand, in the direct writing, a nozzle with a tiny opening is moved over a substrate in accordance with a pre-designed circuit pattern, extruding the paste so as to write a required pattern directly on the substrate. The direct writing requires no step of making a mask having patterns. Accordingly the direct writing takes less time from designing a circuit pattern to form a thick film pattern actually on a substrate than the screen printing.
But the direct writing is not efficient to form patterns having thick lines and large regions, because the patterns have to be formed by laying thin lines.
Furthermore, in the direct writing, in order to keep a film thickness of a pattern constant, on the tip end of the nozzle there is provided a spacer for keeping a gap between a substrate and the tip end of the nozzle constant. But when the spacer comes off a surface of a substrate at an edge thereof, a required gap from the substrate surface to the nozzle can not be kept any more and the movement of the nozzle is limited. Consequently sometimes a required pattern cannot be written.